GANP protein

ABSTRACT

The object of the present invention is to provide a novel protein having a kinase activity and a gene encoding said protein. According to the present invention, there is provided a GANP protein which is represented by the amino acid sequence shown in SEQ ID No. 1 or No. 3 of the sequence listing, and is involved in the signal conversion of abnormal B cell differentiation in an autoimmune state, and has a kinase activity, and a polynucleotide which encodes said protein.

This application is a divisional of application Ser. No. 10/638,333 filed Aug. 12, 2003, now U.S. Pat. No. 6,825,020 B1, which is a divisional of application Ser. No. 09/914,272 filed Dec. 5, 2001, now U.S. Pat. No. 6,673,913 B1, which is a 371 application of PCT/JP99/04634 filed Aug. 27, 1999.

TECHNICAL FIELD

The present invention relates to a novel protein having a kinase activity and a gene encoding said protein.

BACKGROUND ART

Antigen binding to the membrane lgR initiates the activation and maturation of the antigen-specific B cells in the peripheral lymphoid organs (Rajewsky, Nature (Lond.)., 381:751–758, 1996; Sakaguchi et al., Adv. Immunol. 54:337–392, 1993). B cells enter the outer periarterial lymphoid sheath (PALS) (Rajewsky, Nature (Lond.)., 381:751–758, 1996) and initiate costimulus-dependent interactions with specific Th cells and interdigitating dendritic cells within 48 h after immunization (MacLennan, Annu. Rev. Immunol. 12:117–139, 1994; Liu et al., Immunol. Rev. 156:111–126, 1997). Antigen-driven B cells proliferate in the outer PALS and then undergo further activation in the lymphoid follicles to establish the germinal center (herein sometimes abbreviated as GC) (Han et al., J.Immunol. 155:556–567, 1995; Jacob et al., J. Exp. Med. 176:679–687, 1992; Kelsoe, Immunity 4:107–111, 1996). Such B cells mature into large slg⁻ centroblasts that rapidly move through the cell cycle to form the dark zone and further mature into centrocytes that express a unique surface character of PNA⁺B220⁺slgM⁺slgD⁻CD38⁻ in the light zone of the GC (Kosco-Vilbois et al., 1997. Immunol. Today 18:225–230, 1997; Kelsoe, Immunol. Today 16:324–326, 1995; Oliver et al., J. Immunol. 158:1108–1115, 1997).

Centrocytes presumably undergo the processes of either apoptosis or affinity maturation of immunoglobulin V regions and the change process of class switching toward the lgG class antigen. Some centrocytes survive for a longer period in the lymphoid compartment as memory B cells. The other centrocytes probably migrate to the marginal zone of the GC and receive further antigenic stimulation and costimulatory signals through B cell activation molecules, such as CD40 and CD38, and receptors for various B cell stimulatory cytokines (Gray et al., J. Exp. Med., 180:141–155, 1994; Foy et al., J. Exp. Med., 180:157–163, 1994). Antigen-specific B cells further stimulated in this area probably migrate into the interstitial region of the spleen (called red pulp), where various kinds of other immune-competent cells may interact with antigen-driven B cells. Histochemical analysis in several autoimmune mice identified unique antibody-producing cells in this area which appear as plasma cells or aberrant plasma cells called Mott cells (Tarlinton et al., Eur. J. Immunol. 22:531–539, 1992; Jiang et al., J. Immunol., 158:992–997, 1997).

Autoimmunity is a phenomenon in which the impairment of self/nonself discrimination occurs frequently in the antigen-specific lymphocytes (Theofilopoulos, Immunol. Today, 16:90–98, 1995). The immune systems of various autoimmune diseases show the combinatory mechanism involving T cells and B cells (Theofilopoulos et al., Adv. Immunol., 37:269–290, 1985; Okamoto et al., J. Exp. Med. 175:71–79, 1992; Reininger et al., J. Exp. Med., 184:853–861, 1996; Theofilopoulos, et al., Immunol. Rev. 55:179–216, 1981; Watanabe-Fukunaga et al., Nature (Lond.)., 356:314–317, 1992; Takahashi et al., Cell, 76:969–976, 1994; Shlomchick et al., Nature (Lond.). 328:805–811, 1987).

NZB and NZW are the strains characterized by multiple genetic factors generating the severe autoimmune state of SLE as (NZB×NZW)F₁ mice (Theofilopoulos et al., Adv. Immunol., 37:269–290, 1985; Okamoto et al., J. Exp. Med., 175:71–79, 1992; Reininger et al., J. Exp. Med., 184:853–861, 1996; Theofilopoulos et al., Immunol. Rev., 55:179–216, 1981). NZB mice spontaneously generate the state of autoimmunity with the anti-red blood cell antibody that causes an autoimmune hemolytic anemia (Okamoto et al., J. Exp. Med., 175:71–79, 1992). NZW mice show an insidious autoimmune phenomenon (Reininger et al., J. Exp. Med. 184:853–861, 1996). The SLE state of (NZB×NZW)F₁ mice is apparently caused by multiple genetic factors associated with T and B cells (Theofilopoulos et al., Immunol. Rev., 55:179–216, 1981). NZB mice show an apparent abnormality of B cells, but the molecular mechanism of the abnormal B cell activation in NZB mice remains to be elucidated.

DISCLOSURE OF THE INVENTION

To address the issue of which molecules are involved in such maturation of B cells, the present inventors prepared monoclonal antibodies against intracellular components of a murine B cell line WEHI-231, which has the NZB genetic background. A monoclonal antibody named 29–15 recognizes a differentiation antigen whose expression is augmented in GC-B cells of peripheral lymphoid organs. With the 29–15 monoclonal antibody, the present inventors studied the expression of the antigen in peripheral lymphoid organs, which characterized the molecule as a differentiation antigen upregulated in the light zone of the GC from hyperimmunized mice. In the spleen of NZB mice, lgM-producing plasma cells with high expression of the GANP antigen appear before the onset of autoimmunity, which would suggest that this is an important molecular event for understanding the peripheral immune response and autoimmunity with autoantibodies.

The present inventors have studied to identify the above-mentioned antigen whose expression is selectively increased in centrocytes of germinal center, and confirmed by in situ RNA hybridization using an isolated cDNA probe (ganp probe) that the expression of ganp mRNA is increased in the area stained with 29–15 monoclonal antibody. It was also confirmed that the gene product, GANP protein, is a protein of 210 kD which is localized in cytoplasma and nucleus, and is structurally similar with a transcription regulating factor in yeasts, SAC3. When B cells are activated with anti-IgM antibody and anti-CD40 antibody, the amount of kinase which binds to GANP protein increased. These results suggest that GANP protein may be involved in a signal conversion of abnormal B cell differentiation in certain autoimmune state. The present invention has been completed on the basis of these findings.

Thus, the present invention provides a GANP protein represented by the amino acid sequence shown in SEQ ID No.1 or No.3 of the sequence listing. According to the present invention, there is provided a GANP mutant protein which is consisted of the amino acid sequence wherein one or more amino acids are deleted, one or more amino acids are substituted with other amino acid(s), and/or one or more other amino acids are added in the amino acid sequences shown in SEQ ID No.1 or No.3 of the sequence listing, and has a kinase activity similar with that of GANP protein. According to the present invention, there is provided a polypeptide which contains, as a partial sequence, a full length amino acid sequence of the aforementioned GANP protein or the aforementioned GANP mutant protein.

According to another aspect, the present invention provides a polynucleotide which encodes the aforementioned GANP protein or GANP mutant protein. The typical polynucleotide is DNA encoding GANP protein derived from mammal, and the DNA of mammal gene is preferred among them. Examples of most preferred polynucleotide are represented by the base sequences shown in SEQ ID No. 2 (DNA sequence encoding GANP protein from mouse) or SEQ ID No. 4 (DNA sequence encoding GANP protein from human) of the sequence listing.

Further, according to the present invention, there is provided an antisense polynucleotide which is composed of the base sequence of an antisense chain of the aforementioned polynucleotide, or derivatives of said antisense polynucleotide. Furthermore, according to the present invention, there is provided a polynucleotide or antisense polynucleotide of continuous 12 or more bases which is a partial sequence of the aforementioned polynucleotide or the aforementioned antisense polynucleotide, and a chemically modified polynucleotide or antisense polynucleotide of the aforementioned polynucleotide or the aforementioned antisense polynucleotide.

According to further another aspect, the present invention provides a method for obtaining DNA of the base sequence shown in SEQ ID No. 2 or No. 4 of the sequence listing or DNA which is the homologue from other mammal, wherein the aforementioned polynucleotide or antisense polynucleotide is used as a probe, and cDNA which hybridizes to the probe is obtained from mammal cDNA library. The length of the cDNA is almost the same as that of GANP gene, and the protein encoded by it has approximately 210 kDa. Further, according to the present invention, there is provided cDNA obtained by the aforementioned method and GANP protein encoded by it.

According to further another aspect of the present invention, there is provided an antibody which recognizes GANP protein or GANP mutant protein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a photograph showing detection of 29–15⁺ cells in the PP of normal mice. The immunohistochemical analysis was carried out on PP with the 29–15 mAb and ALP-anti-rat lg antibody. Positive cells appear in the central area with Vector Blue ALP substrate, and the strong signal in the surrounding area is in intestinal villi containing nonspecific endogenous ALP activity. For two-color staining, the sections are further stained either with biotin-anti-B220 mAb or biotin-anti-lgD mAb followed by HRP-streptavidin in combination with DAB.

FIG. 2 is a photograph showing appearance of 29–15⁺ cells in the GC area of SRBC-immunized mice. Normal BALB/c mice were injected four times with SRBC during 12 days and the spleen sections were stained with hematoxylin or studied by immunohistochemistry as in FIG. 1. The sections of normal and SRBC-immunized BALB/c mice are parallel, when compared after staining with the 29–15 mAb.

FIG. 3 is a photograph showing appearance of 29–15⁺ cells in the GC area of SRBC-immunized mice. The sections of the GC area are stained with PNA, anti-BrdU, and the 29–15 mAb in combination with the individual colors as described in the Materials and Methods. Upper photograph shows hematoxylin staining of the GC area (GC) and the central artery (CA). Middle photograph shows three-color staining, indicating the 29–15⁺PNA⁺ cells. Lower panel shows a schema of 29–15⁺PNA⁺ cells.

FIG. 4 is a photograph showing expression of the GANP^(dense+) cells in the red pulp area of autoimmune-prone mice. Sections were prepared from the spleens of nonimmunized mice of BALB/c, NOD, NZB, (NZB×NZW)F₁, BXSB, and MRL/lpr. All mice were used 6–8 weeks after birth. The GANP^(dense+) cells stained with the 29–15 mAb appear in the red pulp area of NZB, (NZB×NZW)F₁, MRL/lpr, and BXSB strains.

FIG. 5 is a photograph showing expression of the GANP^(dense+) cells in the red pulp area of autoimmune-prone mice. Sections of the LN of popliteal regions were stained with the 29–15 mAb. The GANP^(dense+) cells appear in peripheral LN of older NZB mice (10 month old) and MRL/lpr mice (8 week old).

FIG. 6 is a photograph showing characterization of the GANP^(dense+) cells in the autoimmune-prone mice. Sections were prepared with the spleen of nonimmunized NZB mice (8 week old). Immunohistochemical analysis was performed with the 29–15 mAb in combination with one of the following reagents: anti-B220, PNA.

FIG. 7 is a photograph showing characterization of the GANP^(dense+) cells in the autoimmune-prone mice. Sections were prepared with the spleen of nonimmunized NZB mice (8 week old). Immunohistochemical analysis was performed with the 29–15 mAb in combination with one of the following reagents: anti-lgM, anti-Syndecan-1, or anti-BrdU mAb.

FIG. 8 is a photograph showing Mott cells that appear in NZB mice by PAS staining.

FIG. 9 is a diagram showing a deduced amino acid sequence of mouse GANP protein in one character notation.

FIG. 10 is a diagram showing a structure of the GANP protein. In the figure, S/T rich region: serine/threonine rich region, SAC3 homology region; SAC3 homology region, nuclear localizing signal: nuclear localizing signal. Four LXXLL motifs are present.

FIG. 11 is a photograph showing a result of in situ RNA hybridization of the ganp gene. Sections of spleens from SRBC-immunized, nonimmunized BALB/c, and NZB mice were hybridized with the ganp anti-sense probe. In the figure, the white pulp area (WP), red pulp area (RP), and GC area (GC) are indicated. The GANP^(dense+) cells were recognized in the red pulp of NZB mice.

FIG. 12 is a diagram showing the results of the analysis by Western blotting after immunoprecipitation of GANP protein. The GANP protein was detected as a 210-kD protein expressed in cytoplasmic and nuclear fractions of WEHI-231 cells.

FIG. 13 is a diagram showing the results where spleen B cells from normal BALB/c mice were stimulated with F(ab′)₂ of goat anti-lgM Ab (10 μg/ml) and anti-CD40 mAb (10 μg/ml) for 48 hour and stained with the anti-GANP mAb.

FIG. 14 is a diagram showing the results where in vitro kinase reaction was carried out with the anti-GANP immunoprecipitates in the presence of [γ-³²P]-ATP for 10 minutes. Phosphorylation on the proteins were detected by the autoradiography after SDS-PAGE separation. Phosphorylation of the GANP is indicated with an arrow (Figure A), and phosphoamino acid analysis of phosphorylated GANP protein is also shown (Figure B).

FIG. 15 is a diagram of the structure of the mouse GANP protein. In the figure, the homologous region to SAC3 and Map80, nuclear localization sequences (NLSs), and coiled-coil regions are indicated. Four LXXLL motifs are indicated by black.

FIG. 16 shows a result of RT-PCR assay. The upregulation of gnap mRNA in anti-μ- and anti-CD40-stimulated B calls in vitro is shown. HPRT was used as a control to confirm the amount of each template.

FIG. 17 shows a result of in vitro kinase reaction. The call lysate was prepared from unstimulated (left) or stimulated (right) cells and subjected to anti-GNAP immunoprecipitation. In vitro kinase reaction was carried out with the anti-GNAP (42–23) immunoprecipitates in the presence of [γ-³²P]-ATP for 10 minutes. Phosphorylation on the proteins was detected by the autoradiography after SDS-PAGE separation. An arrow indicates the position of phosphorylated GNAP.

FIG. 18 is a scheme showing a physical association between GNAP and MCM3. The cell lysate from WEHI-231 was immunoprecipitated with anti-GST, anti-GNAP (42–23), or anti-MCM3 Ab. After separation by SDS-PAGE, the proteins were electrophoretically transferred to a membrane and probed with anti-MCM3 Ab.

FIG. 19 is a scheme showing a physical association between GNAP and MCM3. Anti-GST, anti-GNAP (42–23) and anti-MCM3 immunoprecipitates from WEHI-231 cell lysates were subjected to in vitro kinase assay. Normal rabbit serum (NRS) was used as a control for anti-MCM3 Ab. The samples were separated by 7% SDS-PAGE. The bands corresponding to GNAP and MCM3 were indicated by arrows in the left panel. On the right panel, V8 cleavage mapping of 210-kDa bands showed an identical cleavage pattern. As a control an irrelevant V8-digested protein was separated in parallel.

FIG. 20 is a scheme showing a result where double staining with anti-MCM3 Ab and anti-CR1 mAb, or PNA, was performed. The expression of MCM3 was upregulated in GC area.

FIGS. 21A–B is a scheme where a deduced amino acid sequence of human GANP protein is represented in one character notation.

FIG. 22 is a photograph showing a result where human ganp and Map 80 were mapped by FISH method using human chromosome.

PREFERRED EMBODIMENT FOR CARRYING OUT THE INVENTION

The typical examples of GANP protein of the present invention are protein represented by the amino acid sequences of SEQ ID No. 1 and No. 3 of the sequence listing, and are characterized in that they have a molecular weight of 210 kDa and have a kinase activity. GANP mutant proteins provided by the present invention are represented by the amino acid sequences wherein approximately 1 to several preferably 1 to 20, more preferably 1 to 10, most preferably 1 to 5 amino acid residues are substituted, inserted, and/or deleted in the amino acid sequences of SEQ ID No. 1 or No. 3, and have a kinase activity which is substantially similar with GANP protein represented by the amino acid sequences of SEQ ID No. 1 or No. 2. These GANP mutant proteins are within the scope of the present invention. The protein represented by the amino acid sequences of SEQ ID No. 1 or No. 3 of the sequence listing and homologue thereof are those whose expression is selectively increased in centrocytes of germinal center of mammal from which the protein is derived.

Usually, the active domain of GANP protein or GANP mutant protein can be readily identified by preparing a polypeptide wherein amino acid residue(s) are deleted from N-terminal and/or C-terminal of the full length amino acid sequence, and measuring the kinase activity of the polypeptide. The polypeptides provided by the present invention are those comprised of an active domain of GANP protein and GANP mutant protein and those comprising, as a partial sequence, a polypeptide comprised of said active domain, and have a kinase activity which is substantially similar with GANP protein. Moreover, another polypeptides provided by the present invention are those comprising, as a partial sequence, a full length amino acid sequence of GANP protein or GANP mutant protein, and have a kinase activity which is substantially similar with GANP protein.

The polynucleotide provided by the present invention includes DNA and RNA as well as all of the nucleotides obtained by chemically modifying DNA or RNA. The term “polynucleotide” used herein should be most broadly interpreted to include non-naturally occurring form. The typical examples of the polynucleotide provided by the present invention are DNA or RNA which encodes the aforementioned GANP protein or GANP mutant protein. Another example of the polynucleotide of the present invention is antisense polynucleotide.

It is well known for a skilled person in the art that, using degeneracy of genetic code, at least partial bases of a polynucleotide can be replaced with another type of bases without changing the amino acid sequence of the polypeptide which is produced from the polynucleotide. Therefore, the polynucleotide of the present invention includes all polynucleotides which encode GANP protein or GANP mutant protein. As examples of the preferred gene of the present invention, a gene encoding GANP protein from mouse is shown in SEQ ID No.2 of the sequence listing, and a gene encoding GANP protein from human is shown in SEQ ID No.4. The amino acid sequence of GANP mutant protein can be determined from the base sequence of a gene encoding said mutant. For example, sequencing can be carried out by using commercially available programs (for example, MacVector (registered tradmark, Eastman Chemical), or Genetic (Software Kaihatsu)).

The scope of the present invention covers antisense polynucleotides composed of a base sequence of antisense chain of polynucleotide encoding GANP protein, and derivatives thereof. The antisense polynucleotides is provided as an embodiment of the polynucleotide mentioned above, and the term “antisense polynucleotide” may be herein used to clearly mean that it is a polynucleotide comprised of base sequence of antisense chain. The antisense polynucleotide can hybridize to polynucleotide encoding GANP protein, and if the polynucleotide to which it hybridize is a polynucleotide of coding region, the biosynthesis of the polypeptide encoded by the polynucleotide can be inhibited.

Antisense polynucleotide for inhibiting the biosynthesis of polypeptide preferably contains 12 or more bases. On the other hand, an unnecessarily long sequence is not preferred in order to incorporate full length antisense polynucleotide into cells. When an antisense polynucleotide is incorporated into cells to inhibit the biosynthesis of GANP protein, it is preferred to use an antisense polynucleotide of 12 to 30 bases, preferably 15 to 25 bases, more preferably 18 to 22 bases.

The antisense polynucleotide of the present invention or derivatives thereof include all of the form where several nucleotides composed of base, phosphoric acid and sugar are bound whether or not they are present in nature. Typical examples include a naturally occurring antisense DNA and antisense RNA. Non-naturally occurring polynucleotides include, for example, polynucleotides of methylphosphonate type and phosphorothioate type. As to the antisense polynucleotide of the present invention, various antisense polynucleotide derivatives which are excellent in binding ability to target DNA or mRNA, tissue selectability, cell permeation property, nuclease resistance, intercellular stability and the like, can be obtained by using an antisense technology available to a skilled person in the art.

Generally, in view of easiness of hybridization, it is preferred to design an antisense polynucleotide or derivatives thereof having a base sequence complementary with base sequence which forms a loop of RNA. Therefore, as to the antisense polynucleotide of the present invention and derivatives thereof those which hybridize to loop region of RNA are preferred examples. Moreover, an antisense polynucleotide having a sequence complementary with a translation initiation codon and neighborhood thereof ribosome binding site, capping site, or splicing site can generally be expected to exhibit high expression inhibition effect. Therefore, the antisense polynucleotide of the present invention or derivatives thereof having a sequence complementary with a translation initiation codon and neighborhood thereof, ribosome binding site, capping site, and/or splicing site of the gene encoding GANP protein are preferred example in view of expression inhibition effect.

Among the currently generally known polynucleotide derivatives, the derivatives where at least one of nuclease resistance, tissue selectability, cell permeation property and binding ability is enhanced, preferably include derivatives having a phosphorothioate bond as a skeleton structure. The polynucleotide of the present invention and derivatives thereof include derivatives having these function or structure.

Among the antisense polynucleotide of the present invention, naturally occurring type of antisense polynucleotide may be synthesized by using a chemical synthesizer or may be prepared by a PCR method using a DNA encoding GANP protein as a templeta. Polynucleotide derivatives such as methylphosphonate type or phosphorotioate type may usually be prepared by chemical synthesis. In this case, the procedure can be carried out according to an instruction attached with the chemical synthesizer, and the synthesized product thus obtained-can be purified by HPLC method using reverse phase chromatography and the like.

Polynucleotide which is a polynucleotide encoding GANP protein of the present invention, antisense polynucleotide thereof, or a portion thereof (for example, polunucleotide composed of continuous 12 or more bases) can be used as a probe for screening a DNA encoding GANP protein from mammalian cDNA library. For such a purpose, a polynucleotide composed of a sequence of continuous 15 or more bases is particularly preferred. The polynucleotide used as a probe may be a derivative. Usually, it is recognized that a sequence having the aforementioned number or more of base is a specific sequence.

A DNA of continuous 12 or more bases in the base sequence of SEQ ID No. 2 or No. 4 of the sequence listing, or a polynucleotide which hybridizes to said DNA (antisense polynucleotide) can be used as a probe for screening a DNA encoding GANP protein from cDNA library or the like.

Also, a tissue which expresses mRNA from GANP gene can be detected by performing a Northern Blot hybridization on mRNA derived from various tissues by using a polynucleotide encoding GANP protein of the present invention, antisense polynucleotide thereof, or a polynucleotide of a portion thereof as a probe. Furthermore, a polynucleotide of 12 or more bases can be used as a primer for polymerase chain reaction (PCR), and a polynucleotide encoding GANP protein can be obtained by PCR. Also, the primer can be appropriately selected to clone any portion of GANP protein.

As to the cDNA library used in the screening using the aforementioned probe, one prepared from mRNA can be preferably used. A group of cDNA selected by random sampling from these cDNA library may be used as a sample for screening. A commercially available cDNA library can be used.

The cDNA which hybridizes to the above-obtained GANP gene is inserted into a suitable vector (for example, pGEX-4T-1 vector), and is introduced into a host (for example, E.coli) to prepare a transformant. The type of the vector and the type of the host are not particularly limited, and any suitable expression vector may be selected and used depending on the type of the host. As the host, bacterium such as E.coli, yeasts, or animal cells can be used. A method for obtaining a transformant by introducing a recombinant vector into a suitable host such as E.coli is not particularly limited, and any method available to a skilled person in the art may be applied.

The transformant into which the GANP gene of the present invention was introduced can be cultured to amplify a gene DNA or produce a protein, thereby producing GANP protein. The preparation and culturing of a transformant are described in various literatures and reports, and many methods have been developed and have been conventionally used in the art. Therefore, a skilled person in the art can easily prepare GANP protein on the basis of the base sequence described herein. The methods for introducing a gene into cells include calcium chloride method, lipofection method, protoplast method, and electroporation method.

Separation and purification of a protein of interest from the culture can be carried out by using any means available to a skilled person in the art in combination appropriately. For example, GANP protein of the present invention can be efficiently recovered and purified by performing procedures such as concentration, solubilization, dialysis, various chromatography and the like. More specifically, selection may be suitably made among immunoprecipitation, salting out, ultrafilteration, isoelectric point precipitation, gel filteration, electrophoresis, various chromatography such as ion exchange chromatography, hydrophobic chromatography and antibody chromatography, chromatofocusing, adsorption chromatography, and reverse phase chromatography. By using a gene encoding GANP mutant protein, GANP mutant protein can be similarly prepared.

Also, GANP protein or GANP mutant protein can be prepared as a fused protein with another polypeptide. Such a fused polypeptide is within the scope of the present invention. The type of the polypeptide to be fused is not particularly limited, and includes, for example, a signal peptide which promotes an extracellular secretion. The preparation of such a fused protein may be carried out by using transformant. When a fused protein is used to prepare GANP protein or GANP mutant protein, a fused protein is treated with a chemical substance such as bromecyan or an enzyme such as protease, and the substance of interest which was cut out may be separated and purified.

Antibodies which recognize GANP protein or GANP mutant protein can be prepared by using GANP protein or GANP mutant protein of the present invention or partial polypeptide thereof. The antibody of the present invention can be prepared by any means of a conventional method in the art by immunizing a mammal with GANP protein or GANP mutation protein. It can be confirmed by Western blotting, ELISA, immunostaining (for example, measurement with FACS) or the like that the antibody recognizes GANP protein or GANP mutation protein of the present invention. As immunogens, there may used GANP protein or GANP mutant protein as well as a portion thereof bound to another carrier protein such as calf serum albumin. A portion of GANP protein or GANP mutation protein preferably contains 8 or more amino acid residues, and such a polypeptide may be synthesized by using, for example, a peptide synthesizer.

A monoclonal antibody which is produced from hybridoma prepared by using lymphocytes of immunized animals may be used as an antibody of the present invention. The process for the preparation of a monoclonal antibody is well known in the art and is conventionally used (“Antibodies, A Laboratory Manual” (Cold Spring Harbor Laboratory Press, 1988), Chapter 6). Moreover, a fragment of antibody having a antigen-antibody reaction activity and a chimera antibody may be used as an antibody of the present invention. GANP protein or GANP mutant protein of the present invention can be detected by a method using an antibody or a method using an antibody and an enzyme.

The present invention is illustrated in detail by the examples below, but the scope of the present invention is not limited to the examples below.

EXAMPLE Example 1 Cloning of Mouse GANP Gene and Analysis of Expression

<Materials and Methods>

(1) Animals and Immunization

BALB/c mice and Lewis rats were purchased from Seac Yoshitomi Ltd. (Fukuoka). NZB, NZW, (NZB×NZW)F₁ mice (7 week old, female), MRL/lpr mice (8 week old, female), and BXSB mice (7 week old, male) were obtained from Japan SLC Co. (Shizuoka). Aged NZB mice (10 month old, female) were kindly gifted from Dr. Sachiko Hirose (Department of Pathology, Juntendo University School of Medicine). NOD mice (7 week old, male) were generously provided from Dr. Junichi. Miyazaki (Department of Nutrition and Physiological Chemistry, Osaka University Medical School). All animals were maintained in Center for Animal Resources and Development in Kumamoto University. BALB/c mice were immunized multiply with sheep red blood cells (Nippon Bio-Test Laboratories, Inc., Tokyo). The immunization was performed intravenously with 5-day interval and sections of the thymus, spleen, lymph node (LN), and Peyer's patches (PP) were prepared for the immunohistochemical analysis.

(2) Cells and Cell Culture

Splenic B cells from BALB/c mice were enriched as described previously (Nomura et al., Immunol. Lett. 45:195–203, 1995). These cells were cultured in RPMl-1640 medium (Gibco-BRL, Gaithersburg, Germany) containing 10% heat-inactivated FCS (Dainippon Pharmaceutical Co., Osaka, Japan), 5 mM L-glutamine (Biowhitteker, Walkersville, Md., USA), 100 U/ml penicillin, 100 μg/ml streptomycin, and 50 μM 2-ME at 37° C. in an incubator with 5% carbon dioxide.

(3) Establishment of the 29–15 Monoclonal Antibody (Hereinafter Referred to as “25–15 mAb”)

The mAbs against a murine B cell line WEHI-231, which was established from a (BALB/c×NZB)F₁ mouse with mineral oil, were prepared by the method described previously (Kuwahara et al., J. Immunol. 152:2742–2752, 1994). Briefly, the cell lysate of WEHI-231 with the surface phenotype slgM⁺slgD⁺B220⁺ was prepared with the hypotonic buffer in the absence of detergent and dialyzed against a phosphate buffered saline (PBS) in accordance with the method of Sakaguchi et al (Sakaguchi et al., EMBO (Eur. Mol. Biol. Organ.) J. 5:2139–2147, 1986). The cell lysate was immunized into the foot pads of Lewis rats in the complete Freund's adjuvant (CFA) (Difco Laboratories, Detroit, Mich., USA) and boosted twice in the incomplete Freund's adjuvant (IFA) (Difco Laboratories) at day 4 and day 8. After 9 days, the lymph node of popliteal and inguinal regions were excised and the lymphoid cell suspension was prepared. Establishment of hybridomas, selection in the HAT media (Gibco-BRL), and recloning of hybridoma clones were performed as described previously (Kuwahara et al., J. Immunol. 152:2742–2752, 1994). The 29–15 mAb was selected to stain lymphoid cells in the immunohistochemical analysis.

(4) Antibodies and Reagents

F(ab′)₂ fragment of the affinity-purified goat anti-mouse μ antibody (ICN Pharmaceutical, Inc., Costa Mesa, Calif., USA), biotin-conjugated peanut agglutinin (PNA) (Vector Laboratories, Inc., Burlingame, Calif., USA), biotin-conjugated anti-CD35 mAb (PharMingen, San Diego, Calif.), alkalinephosphatase (ALP) conjugated goat anti-rat IgAb (#59301, ICN), HRP conjugated goat anti-rat IgAb (ICN), HRP conjugated streptavidin (Kirkegaard & Perry Laboratories, Inc., Gaitherburg, Md.), ALP conjugated goat anti-mouse IgAb (Sigma Chemicals Co., St. Louis, Mo.), FITC conjugated mouse anti-rat κ mAb (ICN), PE conjugated anti-B220 mAb (PhaMingen), and ALP conjugated goat anti-rabbit IgAb (Zymed Laboratories Inc., South San Francisco, Calif.) were purchased and used. Biotin-conjugated mAbs such as anti-B220 (RA3-6B2), anti-μ (AM/3), and anti-δ (CS/15) were prepared in our laboratory. Anti-CD40 mAb (LB429) was established in our laboratory (Nomura et al., Immunol. Lett. 45:195–203, 1995). Hybridomas of AM/3 and CS/15 were kindly provided by Dr. Kensuke Miyake (Department of Immunology, Saga Medical School). Biotin-conjugated anti-Syndecan-1 was purchased from PharMingen (San Diego, Calif., USA). Anti-BrdU mAb was obtained from Novocastra Laboratories, Ltd. (Newcastle, United Kingdom). Rabit anti-mouse MCM3/P1 Ab is described in the literature (Kimura, H et al, 1994, EMBO J. 13, 4311–4320).

(5) Immunohistochemistry

Immunohistochemical staining was performed as described previously (Ezaki et al., Arch. Histol. Cytol. 58:104–115, 1995; Yamanouchi et al., Eur. J. Immunol. 28:696–707, 1998). In brief, the target organs excised from BALB/c, NZB, (NZB×NZW)F₁, NOD, BXSB, and MRL/lpr mice were placed in OCT compound (Miles Inc., Elkhart, Ind., USA). The 6-μm cryosections placed on the gelatin-coated slides were air-dried fully. The slides were then fixed in acetone for 10 minutes, followed by rehydration in PBS for 15 minutes. The slides were incubated with the 29–15 mAb for 60 minutes and were washed with PBS several times. After incubation with alkaline phosphatase-conjugated goat anti-rat lg antibody (ALP-anti-rat lg, catalogue #59301, ICN Pharmaceutical, Inc.), the slides were washed four times with PBS. The slides were developed using Vector Blue (Vector Laboratories).

For secondary staining, the slides were incubated with biotin-labeled mAbs in combination with horseradish peroxidase (HRP)-conjugated streptavidin (Kirkegaard & Perry Laboratories, Inc., Gaithersburg, Md., USA). After development with p-dimehylaminoazobenzene (DAB, Dojindo, Kumamoto), the sections were fixed lightly with 1% glutaraldehyde solution in PBS. To detect the cells of active proliferation in vivo, BrdU (Sigma Chemicals Co., St. Louis, Mo., USA) was injected intravenously 1 hour before obtaining the organs. Cells undergoing DNA synthesis were detected by staining with anti-BrdU mAb in combination with ALP-conjugated goat anti-mouse lg Ab (Sigma Chemicals Co.) followed by development with Vector Red (Matsuno et al., Cell Tissue Res. 257:459–470, 1989). Periodic acid Schiff (PAS) staining was performed as described previously (Jiang et al., J. Immunol. 158:992–997, 1997). All sections were mounted by Aquatex (E. Merck, Darmstadt, Germany).

(6) Molecular Cloning of the cDNA Using λgt11 Vector

The cDNA libraries constructed with mRNAs from the mouse spleen, mouse bone marrow, WEHI-231 cells and A20 cells were screened with the supernatant of the 29–15 mAb after transferring the fusion protein onto nitrocellulose filters (Schleicher and Schuell, Darmstadt, Germany) that were presoaked with 20 mM IPTG (Inui et al., J. Immunol. 154:2714–2723, 1995). The phage plates were incubated for 4 hours at 42° C. and then the plates were covered with the filters and further incubated for 4 hours at 37° C. The filters were washed three times with the washing buffer (PBS containing 0.1% Tween 20), blocked for 1 hour in the blocking buffer (5% nonfat dry milk in PBS containing 0.1% Tween 20), and then incubated with the 29–15 mAb. Positive signals were detected by autoradiography using ¹²⁵l-labeled sheep anti-rat lg Ab (Amersham, Buckinghamshire, United Kingdom). The initial cDNA clone contained a 280-bp fragment that is capable of coding a polypeptide as a fusion protein. With the original 280-bp fragment, the longer cDNA clones were isolated from another WEHI-231 cDNA library. The 4.9-kb fragment of the second cDNA clone encodes a longest open reading frame of 4.5 kb. To further determine the 5′ sequence, the 5′-RACE method was employed. The race kit of Gibco-BRL was used.

(7) In situ RNA Hybridization on Tissue Sections

In situ RNA hybridization was carried out as described previously (Kondo et al., Blood 80:2044–2051, 1992). Paraffin-embedded sections were mounted on silanized slides. After the slides were deparaffinized, hybridization with ganp 280-bp riboprobe labeled by digoxigenin was performed for 16 hours at 50° C. The slides were washed with TNE buffer (10 mM Tris-HCl [pH 7.6], 500 mM NaCl, 1 mM EDTA) at 37° C. several times, followed by washing with 2× and/or 0.2×SSC solution at 50° C. While using anti-digoxigenin antibody, the development was performed in the presence of ALP substrate.

(8) Preparation of GST-cDNA Fusion Protein and Another Anti-GANP mAb

The ganp cDNA fragment encoding a part of GANP (amino acids of 679th to 1028th of the amino acid sequence of SEQ ID No.1 of the sequence listing) was introduced into a pGEX-4T-1 vector (Pharmacia Biotech, Piscataway, N.J., USA). The recombinant plasmid was verified by DNA sequencing of the entire insert and the junction. The GST-GANP fusion protein was prepared by glutathione-Sepharose (Pharmacia) column chromatography as described elsewhere (Inui et al., J. Immunol. 154:2714–2723, 1995). Anti-GANP mAb, designated 42–23, was established by immunizing the fusion protein in rats as described above.

(9) Western Blot Analysis

Protein gel electrophoresis, Western blot transfer, and the immunodetection of proteins were performed as described previously (Kuwahara et al., Int. Immunol. 8:1273–1285, 1996). Fifty million cells were lysed with 1 ml of the TNE lysis buffer (10 mM Tris-HCl [pH 7.8], 150 mM NaCl 1 mM EDTA, 1% NP-40, 0.02% NaN₃) and the immune complex was analyzed on SDS-PAGE (7%). After the proteins were transferred onto a nitrocellulose filter, the filter was blocked with PBS-Tween 20 containing 5% nonfat dry milk and incubated with anti-GANP mAb for 60 minutes. After washing with PBS-Tween 20 several times, the filter was incubated with HRP-conjugated goat anti-rat lg (ICN Pharmaceutical, Inc.) for 30 minutes. The development was performed using an ECL detection kit (Amersham).

(10) Subcellular Fractionation

Separation of intact nuclei was carried out as described previously (Schriber et al., Nucleic Acids Res. 17:6419, 1989). WEHI-231 cells were washed with TBS and the pellets were resuspended in buffer A (10 mM HEPES [pH 7.9], 10 mM KCl, 0.1 mM EDTA, 0.1 mM EGTA, 1 mM DTT, 0.5 mM PMSF) and incubated for 15 minutes on ice, followed by the addition of NP-40 to a final 1%. After the centrifugation, the supernatants were recovered as a cytoplasmic fraction. The pellets were resuspended with the same buffer and homogenized to obtain the intact nuclei by staining. The sample was centrifuged and the pellet was resuspended with cold buffer C (20 mM HEPES [pH 7.9], 0.4 M NaCl, 1 mM EDTA, 1 mM EGTA, 1 mM DTT, 1 mM PMSF) and centrifuged. The supernatants were frozen at −80° C. as a nuclear fraction.

(11) In Vitro Kinase Reaction and Phosphoamino Acid Analysis

Kinase reaction was carried out in vitro with the immunoprecipitate as described previously (Kuwahara et al., J. Immunol. 152:2742–2752, 1994). Splenic B cells were purified by the method described (Nomura et al., Immunol. Lett. 45:195–203, 1995). The B cells were stimulated in vitro for 48 hours with F(ab′)₂ fraction of goat anti-lgM Ab and anti-CD40 mAb (LB429) as described previously (Nomura et al., Immunol. Lett. 45:195–203, 1995). After harvesting and washing, cells were lysed with TNE Iysis buffer and immunoprecipitated with the anti-GANP mAb (42–23). The immunoprecipitates were incubated with [γ-³²p]-ATP (Amersham) and the radiolabeled proteins were analyzed on SDS-PAGE (7%) and with autoradiography. The band corresponding to GANP was excised from dried gel. After SDS was removed from the gel, the homogenized gel was digested by TPCK-trypsin (Sigma Chemicals Co.) at 37° C. overnight. The samples were subjected to hydrolysis with 6N HCl and electrophoresed onto TLC (E. Merck).

V8 cleavage mapping of the indicated proteins was carried out as described previously (Kuwahara, K., et al, 1994, J. Immunol. 152:2742–2752).

(12) Cytoplasmic Staining

The cells were fixed with 2.5% paraformaldehyde solution in PBS followed by permeabilization with 70% ethanol for 1 hour on ice. The cells were incubated with the 29–15 mAb in combination with FITC-conjugated mouse anti-rat κ mAb. Antibody-binding was analyzed on FACScan flow cytometer (Becton-Dickinson, Mountain View, Calif., USA).

(13) Immunoprecipitation and Western Blot Analysis

Proteins obtained in the aforementioned (10) subcellular fractionation were immunoprecipitated with the anti-GABP mAb in combination with protein G-Sepharose, and analyzed by SDS-PAGE. The Western blot filter was incubated with the anti-GANP mAB, followed by HRP-anti-rat Ig. The development was performed using an ECL detection kit (Amersham).

(14) Reverse Transcriptase-PCR (RT-PCR)

Total RNA (1 μg each), purified from cultured B cells using TRISOL (Gibco BRL, Rockville, Md.) was used as a template for the cDNA synthesis (100 μl volume) with Superscript (Gibco BRL). PCR amplification was carried out using 2 μl of each cDNA solution with Taq-Gold (Perkin-Elmer, Foster, Calif.) and the primers for ganp or HPRT (control) (Han, S., et al, 1996, Science. 274–2092–2097). The ganp transcripts were amplified by 5′-CCGTGGGATGACATCATCAC-3′ (the forward primer) (SEQ ID No. 5 of the sequence listing) and 5′-CATGTCCACCATCTCCAGCA-3′ (the reverse primer) (SEQ ID No. 6 of the sequence listing).

<Results>

(1) Expression of the GANP Antigen in Lymphoid Organs

An mAb that recognizes a differentiation antigen expressed in peripheral B cells was prepared by immunizing rats with the lysate of WEHI-231 cells. Immunohistochemical analysis with the 29–15 mAb on normal lymphoid organs of BALB/c mice did not detect expression in the bone marrow, but showed the slight expression in lymphoid organs such as the thymus, spleen, and lymph node. A small number of cells in the red pulp of the spleen and the deep cortex of the lymph node strongly express the 29–15 Ag. Interestingly, the expression was very high in the central area of follicles of the PP (FIG. 1). The cells were positive with anti-B220 mAb, but not with anti-lgD mAb. Normal mice show the development of secondary lymphoid follicles with clear GC in PP because of the continuous stimulation of various antigenic substances introduced through the intestinal lumen.

Repeated immunization with sheep red blood cell (SRBC) induces the formation of lymphoid follicles in the spleen within 12 days. Antigen immunization induces an appearance of 29–15⁺ cells in the GC area of the spleen and lymph node as well as in the GC of the PP (FIG. 2). The 29–15 antigen appeared upregulated in cells of the GC. The phenotype of 29–15⁺ cells in the architecture of secondary lymphoid follicles was further analyzed. Nearly half of PNA⁺ GC-B cells are positive with the 29–15 mAb, but they are negative with anti-BrdU mAb (FIG. 3). Interestingly, the expression of 29–15 Ag is upregulated in the centrocyte area at the distal region of the entrance from the central artery. This phenotype is consistent with the criteria of GC-B cells and supports the name “GANP” for the 29–15 Ag as described above.

(2) Appearance of GANP^(dense+) B Cells in the Red Pulp-Area of Autoimmune-prone NZB Mice

Normal mice express few GANP⁺ B cells in the follicular area of the spleen without in vivo stimulation but show a few GANP^(dense+) cells which remarkably express GANP protein in the red pulp area of BALB/c (FIG. 2) and C57BL/6. These cells are large and obviously different from conventional B cells. In young (8 week old) NZB mice, however, these GANP^(dense+) cells increased spontaneously in the red pulp area of the spleen without immunization (FIG. 4). Another autoimmune-prone mouse, NZW, does not express GANP^(dense+) cells in the red pulp at ages of 5 to 12 weeks. A severe-disease combination of (NZB×NZW)F₁ shows an intermediate expression of GANP^(dense+) cells in the red pulp.

Whether the GANP^(dense+) cells also appear spontaneously in the spleen of other autoimmune-prone mice was examined. The GANP^(dense+) cells appear in the spleen of BXSB and MRL/lpr, but not markedly in NZW and NOD mice at a similar age in the specific pathogen free condition (SPF). The GANP^(dense+) cells become apparent during aging and appear in the peripheral lymph node of the aged-NZB mice (10 month old) that have passed the onset of the disease. The appearance of the GANP^(dense+) cells in the lymph node seems to be mostly in the later stage. Of particular interest, MRL/lpr shows the appearance of GANP^(dense+) cells in the lymph node at the young stage (8 week old)(FIG. 5). These results suggested that a genetic factor in autoimmune-prone NZB, BXSB, and MRL/lpr mice might control the appearance of GANP^(dense+) cells in the red pulp area and the recruitment into the lymph node.

Two-color analysis showed the phenotype of GANP^(dense+) cells in the red pulp area as PNA⁻B220⁻ cells (FIG. 6) and IgD-CD38⁻ cells. These cells are positive when stained with anti-Syndecan-1 mAb, which stains plasma cells selectively. The GANP^(dense+) cells express IgM in cytoplasm (FIG. 7). Because these cells could be Mott cells (Jiang, Y., S. Hirose, Y. Hamano, S. Kodera, H. Tsurui M. Abe, K. Terashima, S. Ishikawa and T. Shirai. 1997. J. Immunol. 158:992–997.), the section was stained with PAS staining. The GANP^(dense+) cells show PAS⁻, as with the B220-Syndecan-1⁺PNA⁻ BrdU⁻GANP^(dense+) (FIG. 8) and CD40⁻CD38⁻. These plasma-like cells appear preferentially in the spleen of NZB mice, but are different from Mott cells currently reported .

(3) Identification of a cDNA Clone Encoding the GANP Antigen

Using the 29–15 mAb, we isolated a candidate cDNA clone (with the insert DNA of 280 bp) from the WEHI-231 cDNA library and further isolated a longer cDNA clone, named ganp. The full-length nucleotide sequence (6429 bp) determined from overlapping clones shows a putative polypeptide composed of 1971 amino acids with a predicted molecular size of 210-kD (FIG. 9). The amino acid sequence of GANP protein is shown in SEQ ID No. 1 of the sequence listing and the base sequence of ganp cDNA is shown in SEQ ID No. 2 of the sequence listing.

The GANP amino acid sequence shows a regional homology to SAC3 which is considered to be a nuclear transcription regulation factor characterized in temperature-mutant Saccharomyces cerevisiae and human Map 80 protein (Takei, Y et al,. 1998, J. Biol. Chem. 273:22177–22180) (FIG. 10 and FIG. 15; Bauer, A. and R. Koelling. 1996. Yeast 12:965–975). The GANP protein shows mild homologies within short stretches of the insulin promoter factor (amino acids 996 to 1063) and various transcription factors, including NF-IL-6 (amino acids 388 to 450).

The GANP gene shows a consensus base sequence for the super coil motifs, but does not show zinc-finger, leucine-zipper, and homeo-domain motifs. A serine/threonine-rich region was seen in N-terminal 100 amino acids, which has slight homology to nucleoporin, which is known as the nuclear pore complex. GANP has two possible nuclear localization sequences (⁴⁹⁷HKKK and ¹³⁴⁴PMKQKRR), which would potentially support the expression of the GANP in the nucleus as suggested by the PSORT program. Moreover, GANP has 2 coiled-coil motifs, but does not have zinc-finger, leucine-zipper, and homeo-domain motifs. Further, there were 4 LXXLL motifs which were recognized in nuclear transcription coactivator molecules including CBP/p300 and p/CIP (Torchia, J. et al., 1997. Nature (Lond.) 387:677–684; Heery et al., 1997, Nature (Lond.) 387:733–736), but any association molecule through these motif. has not been identified.

(5) Expression of the Ganp Transcripts

Northern blot analysis detected the 7-kb mRNA as a very weak signal in comparison to the control β-actin signal, but its expression was rather ubiquitous in all cell lines, organs, and tissues tested. In order to examine whether the ganp mRNA is upregulated in the same areas as detected on sections with the 29–15 mAb, in situ RNA hybridization analysis was carried out. The ganp mRNA is expressed abundantly in the central area of the GC of the SRBC-immunized spleen, but not in the nonimmunized spleen (FIG. 11), thymus, and lymph node. The ganp mRNA was upregulated in GC-B cells of immunized mice. This expression pattern is quite similar to the results with the 29–15 mAb on the same section based on staining with hematoxylin. The GC area of the PP also showed upregulation of the ganp mRNA in nonimmunized BALB/c mice, and the expression of ganp mRNA is high in plasma-like cells of the red pulp area of the spleen of nonimmunized NZB mice (FIG. 11). These results suggests that the ganp gene encodes a molecule recognized by the 29–15 mAb.

(6) Expression of the GANP in B Cells

The anti-GANP mAb (42–23) detected a single protein band at 210-kD from both nuclear and cytoplasmic compartments of WEHI-231 cells (FIG. 12). In order to find evidence of the functional involvement of the GANP in the activation and differentiation of B lineage cells, B cells from nonimmunized BALB/c mice were stimulated in vitro with anti-lgM and anti-CD40 in combination, and as a result, an expression of the GANP protein detected with the anti-GANP mAb was increased (FIG. 13). An in vitro kinase reaction with the GANP immunoprecipitates showed an increased kinase activity assembled with the GANP protein in spleen B cells stimulated in vitro. Thus, the GANP protein is inducibly phosphorylated at the serine/threonine residues (FIG. 14). These results suggest that the GANP might play a role to the activation of B cells in peripheral immune responses.

Stimulation with anti-μ Ab and anti-CD40 mAb showed maximal response, but either one of these regents showed only a marginal response (data not shown). This upregulation was also detected by the increase of ganp mRNA in B cells stimulated by anti-μ and anti-CD40 co-ligation in vitro (FIG. 16). RT-PCR clearly demonstrated that the amount of ganp mRNA increased at 24 hours and 48 hours after stimulation in comparison with the control HPRT mRNA.

Since the 210-kDa GANP has many possible phosphorylation sites, we examined the induction of phosphorylation by an in vitro kinase reaction with anti-GANP immunoprecipitates. As shown in FIG. 17, phosphorylation of the 210-kDa protein was found in the anti-GANP immunoprecipitates from spleen B cells stimulated by anti-μ and anti-CD40 co-ligation. This result indicates that a kinase activity is maintained even if GANP is precipitated.

(7) Association of GANP with MCM3 Protein

We found a Map80-homologous region (76.3% identity at amino acid level) in the carboxyl-terminal part of GANP. Map80 is an 80-kDa nuclear protein that is involved in the translocation of MCM3 (a protein essential for DNA replication) between the cytoplasm and the nuclei (Takei, Y. et al, 1998, J. Biol. Chem. 273:22177–22180; Kimura, H. et al, 1994, EMBO J. 13:4311–4320; Chong, J. P. et al, 1996, Trends. Biochem Sci. 21:102–106; and Romanowski, P et al, 1996, Curr. Biol. 6:1416–1425). Therefore, we examined the interaction between GANP and MCM3 in WEHI-231. We detected that anti-GANP immunoprecipitates include MCM3. Because the phosphorylation states of MCM proteins seem crucial in regulation of cell cycle progression (Kimura, H. et al, 1994, EMBO J. 13:4311–4320; Chong, J. P. et al, 1996, Trends Biochem Sci. 21:102–106; and Romanowski, P et al, 1996, Curr. Biol. 6:1416–1425), in vitro kinase assays with anti-MCM3 immunoprecipitates was performed. Immunoprecipitation of MCM3 co-precipitated a phosphorylated protein migrated at 210-kDa, which is the identical size of GANP (FIG. 19, left panel). These 210-kDa bands from anti-GANP and anti-MCM3 immunoprecipitates showed an identical pattern in the V8 cleavage mapping (FIG. 19, right panel), indicating that GANP and MCM3 are associated in a B cell line.

Next, we studied whether MCM3 is upregulated in GC-B cells by antigen-immunization of mice in vivo. The contiguous sections to those used above were stained with the anti-MCM3 Ab (FIG. 20). MCM3 is also upregulated in GCs. Double staining clearly demonstrates the co-localization of both MCM3 and PNA. A part of GC area is surrounded intensely with FDCs (lymph follicular cells). These results demonstrate that MCM3 is upregulated in GC-B cells including centroblasts and the GANP⁺ centrocytes that would be mostly surrounded by FDCs (FIG. 20).

(8) Discussion

As mentioned above, the present inventors found a novel protein, GANP, expressed in GC-B cells localized at the light zone of secondary follicles in the spleen. Although a trace amount of the ganp mRNA is detectable in many kinds of cells under normal conditions, the GANP protein appears upregulated in the specified GC area of immunized mice. A number of studies demonstrated various differentiation antigens in the GC as molecules recognized with mAbs or by specific cDNA cloning (Christoph et al., Int. Immunol. 6:1203–1211, 1994; Li et al., Proc. Natl. Acad. Sci. USA. 93:10222–10227, 1996; Kuo et al., J. Exp. Med. 186:1547–1556, 1997). Most molecules appear in GC-B cells of the whole area, whereas 8-oxoguanine DNA glycosylase is expressed in the dark zone (Kuo et al., J. Exp. Med. 186:1547–1556, 1997).

Interestingly, the GANP antigen is selective in the centrocyte of the light zone. Recent studies have shown that RAG protein which is necessary for rearrangement of immunoglobulin gene is selectively expressed in centrocytes at the light zone (Hikida et al., 1996. Science (Wash. D.C.) 274:2092–2094, 1996; Han et al., Science (Wash. D.C.) 274:2094–2097, 1996). Since the GC area-probably provides the site for secondary lg gene rearrangement occurring during T cell-dependent antibody responses, as described by Papavasiliou et al. and Han et al. (Papavasiliou et al., Science (Wash. D.C.), 278:298–301, 1997; Han et al., Science (Wash. D.C.), 278: 301–305, 1997), the GANP protein might be a component associated with the maturation of antigen-specific B cells at the centrocyte stage.

We found that the carboxyl-terminal portion of GANP has a significant similarity to human Map80, which facilitates the nuclear transport of MCM3 (Takei, Y et al., 1998, J.Biol.Chem.273:22177–22180). Immunoprecipitation experiments demonstrated that GANP also binds to MCM3 in WEHI-231. MCM3 is a member of the MCM protein family essential for the initiation of DNA replication (Kimura, H. et al, 1994, EMBO J. 13:4311–4320; Blow, J. J. 1993. J.Cell Biol.122.993–1002; Tye, B. K 1994. Trends Cell Biol. 4: 160–166; Chong, J. P. et al, 1996, Trends Biochem Sci. 21:102–106; Romanowski, P et al, 1996, Curr. Biol. 6:1416–1425; and Thommes, P et al, 1992, Nucl. Acids Res. 20: 1069–1074). The major fractions of nuclear MCM proteins bind to chromatin at the beginning of the S phase, but dissociate during replication and accumulate as free proteins in the nucleosol. The release of MCMs from chromatin is accompanied by the phosphorylation of several MCM proteins and their reassociation after mitosis is concomitant with their dephosphorylation. It was suggested that MCM proteins are no longer synthesized in growth arrested, differentiating cells and disappear with kinetics related to their half-life (Musahl, C., et al, 1998, Exp.Cell.Res. 241, 260–264). The MCM3 protein has recently been shown to an early target in apoptotic proteolysis (Schwab, B. L. et al., 1998, Exp.Cell Res. 238:415–421). Schwab, B. L. et al proposed that active destruction of MCM3 inactivates the MCM complex and serves to prevent untimely DNA replication events during the execution of the cell death program. Our results showed that GC-B cells express high level of MCM3, some of which is associated with GANP. However, it appears curious that a protein, upregulated in differentiated cells that arrest the cell cycle, binds to another protein essential for progression of the S phase. One possible speculation is that a function of GANP may be inactivation of MCM3 through its binding. The immunohistochemistry data are consistent with the following idea; GANP is upregulated in growth-arrested centrocytes while MCM3 is expressed both in rapid-cycling centroblasts and still in centrocytes in GCs. Although the amount of MCM3 would decrease by ceasing the gene expression and active destruction (Musahl, C., et al, 1998, Exp.Cell.Res. 241, 260–264; and Schwab, B. L. et al., 1998, Exp.Cell Res. 238:415–421), inactivation of MCM3, which is still expressed in centrocytes, through the interaction with GANP could be another mechanism to prevent DNA replication. In addition, both GANP and MCM3 become phosphorylated with the co-precipitated kinase (FIG. 19). Since the highly phosphorylated MCM3 is thought to be inactivated form (Kimura, H. et al, 1994, EMBO J. 13:4311–4320), the association with GANP may stimulate phosphoryltion of MCM3.

The GANP protein has a close similarity to the SAC3 (SAC, suppressor of actin) of yeasts, Saccharomyces cerevisiae, which was isolated in a genetic screen for suppressors of a temperature-sensitive mutation (act1-1) in the actin gene (FIG. 10; Novick et al., Genetics, 121:659–674, 1989). The SAC3 protein is expressed in the nuclei and is required for normal progression of mitosis and protection against the loss of chromosomes (Bauer et al., J. Cell. Sci. 109:1575–1583, 1996). Null mutants of SAC3 grow very slowly and are larger than wild-type cells. SAC3 participates in a process that affects both the actin cytoskeleton and mitosis, which suggest that SAC3 regulates the gene expression of actin or actin-binding proteins.

A gene (named LEP-1) that augments the transcription of the leucine permease activity in Saccharomyces was identical to SAC3 (Stella et al., Yeast 11:460–460, 1995). Although the LEP-1 gene induces the upregulation of the yeast leucine permease involved in selective amino acid transport, the amino acid transport in eukaryotic cells, especially the molecules involved in amino acid permeation is not known (Mastroberardino et al., Nature (Lond.) 395:288–291, 1998). Although the SAC3/LEP-1 sequence does not show motifs homologous to a number of transcription factors, the biological functions determined previously (Bauer et al., J. Cell. Sci. 109:1575–1583, 1996) suggest its regulatory activity of various target genes in the nucleus. The mouse GANP does not show typical consensus motifs for nuclear transcription factors, but has a common ancestor with SAC3 gene of yeasts and has structural similarity of possible phosphorylation sites, two nuclear localization sequences, and two super coil structures that might interact with other transcription molecules.

GANP is selectively upregulated in centrocytes of Ag-immunized spleen. It is also useful as the differentiation marker to define the centrocyte subset that is closely interacting with FDCs in GC area. Our study showed that the BCR signal and the CD40 co-stimulation together cause the upregulation of GANP and lead to the signal transduction mediated through GANP/MCM3 complex.

The defective gene in the autosomal recessive genetic disease autoimmune polyendocrinopathy (APECED) is localized by linkage analysis to human chromosome 21 (21q22.3), which encodes an AIRE gene product with a possible transcription regulator (Nagamine et al., Nature Genet. 17:393–398, 1997). The autoantibody recognizes the AIRE protein expressed in the adrenal gland and other gonad-producing tissues. Studies of APECED drew an idea that the involvement of molecules with nuclear coactivator activity might be associated with the autoimmunity. Both the AIRE and GANP proteins do not have typical domains for transcription regulators, but they have LXXLL motifs as similarly observed in nuclear transcriptional coactivators.

A B cell-specific nuclear coactivator (Bob1/OCA-B/OBF1) was recently characterized as a cell-type-specific regulator of Oct1 and Oct2 (Luo et al., Mol. Cell. Biol. 15:4115–4124, 1995). The OCA-B targeted mice show the impairment of the GC formation in the spleen after immunization with T-dependent antigen, which suggests the functional involvement of B cell maturation in the GC area (Kim et al., Nature (Lond.) 383:542–547, 1996; Qin et al., EMBO J. 17:5066–5075, 1998). The expression of the GANP protein might be under the control of the OCA-B cell in centrocytes. The molecular interaction of the nuclear coactivator molecules would be an important issue for the understanding of the B cell maturation in the GC.

The New Zealand model of SLE has been the experiment subject of genome linkage studies to map the chromosomal positions of disease-susceptibility genes. At least 12 non-MHC loci linked with nephritis and autoantibody production such as on chromosome 4 (designated Nba1), on chromosome 7, and on chromosome 1 (designated as Nba2; Vyse et al., J. Immunol. 158:5566–5574, 1997) have been independently mapped. The GANP antigen on large cells is highly upregulated in the red pulp area of the nonimmunized NZB mice (FIGS. 4–8). NZB mice contained similar large lgM-producing cells, named Mott cells, in the red pulp area. Mott cells appear selectively in NZB and (NZB×NZW)F₁ mice, but not in normal BALB/c or C57BU/6 mice.

The precursor cells of Mott cells are probably B-1 B cells (Tarlinton et al., Eur. J. Immunol. 22:531–539, 1992; Jiang et al., J. Immunol. 158:992–997, 1997), which suggests a close association with the autoimmunity of B cells. Mott cells are apparent with the inclusion body of lgM in the cytoplasm and positive staining with PAS (Tarlinton et al., Eur. J. Immunol. 22:531–539, 1992; Jiang et al., J. Immunol. 158:992–997, 1997). Because GANP^(dense+) cells seem to be Mott cells, PAS staining was performed. However, GANP^(dense+) cells in the red pulp area of NZB mice are PAS⁻. The GANP^(dense+) lgM-producing cells appear in the spleen of NZB mice, as do Mott cells, but these cells are different. The new type of lgM-producing cells could be generated by the possible activation of an abnormal B cell population related to one of the chromosomal loci linked to disease-susceptibility.

Lyn^(31/−) mice and CD40L^(−/−) mice reported from several laboratories show similar autoimmunities and hyper-lgM syndrome(s), which have an increased appearance of immunoblast cells with the inclusion body in the spleen (Hibbs et al., Cell 83:301–311, 1995; Nishizumi et al., Immunity 3:549–560, 1995; Xu et al., Immunity 1:423–431, 1994). These observations suggest that the signal transduction through BCR and CD40 is regulating the generation of the abnormal antibody-producing plasma cells. Stimulation of splenic B cells with anti-lgM and anti-CD40 antibodies induces the phosphorylation activity of the GANP protein. This observation suggests that the GANP protein may be involved in downstream of the B cell activation site in the GC area and the abnormal B cell activation in NZB mice might be associated with the increased expression of GANP protein.

Example 2 Cloning of Human GANP Gene

On the basis of information of the sequence of rat GANP gene, human GANP gene was cloned and sequenced. Specifically, λgt 11-human heart cDNA library (Clontech) was used, and gsp1-1: TTTGTCTGGAGGATGATCGC (SEQ ID No.7 of the sequence listing), gsp1-2: AAAGAGAAAGGGGCCAGGCC (SEQ ID No.8 of the sequence listing) and gsp1-3: CCAGCTTCTTGTCCAAAAGC (SEQ ID No.9 of the sequence listing) were used as primers, and 5′ RACE System for Rapid Amplification of cDNA Ends, Version 2.0(Gibco BRL) was used to carry out the cloning and sequencing by a conventional method.

The base sequence of the obtained clone was determined. The base sequence of the obtained human GANP gene is shown in SEQ ID No.4 of the sequence listing. The amino acid sequence encoded by this base sequence is shown in SEQ ID No.3 of the sequence listing and FIG. 21. Human GANP gene shows high homology with mouse GANP gene, and Human GANP contains Map80 domain of 80 kDa at carboxyl terminal.

In in situ RNA hybridization, ganp transcript seems to be activated at GC region of tonsil. GANP⁺ cells express CD38⁺IgD⁺ phenotype of memory B cell. These results show that human GANP is expressed also in GC-B cells of secondary lympho tissues. Moreover, since human GANP of 1980 amino acids has a stretch of Map80 homologous region which binds to MCM3 protein in B cells, it is suggested that GANP is involved in the regulation of cell cycle in GC-B cells.

Furthermore, in situ hybridization was carried out by FISH method with the obtained human GANP gene and human chromosome specimen. The results are shown in FIG. 22. As is understood from FIG. 22, the genome fragment containing human GANP gene and Map80 was mapped on 22.3 of the long arm of chromosome 21.

INDUSTRIAL APPLICABILITY

The protein of the present invention is a novel protein having a kinase activity, and may be involved in a signal conversion of abnormal B cell differentiation in an autoimmune state. Therefore, the protein, polypeptide, polynucleotide, antisense polynucleotide and antibody of the present invention are useful for revealing the mechanism of autoimmune. 

1. An isolated polynucleotide which encodes a protein having the amino acid sequence shown in SEQ ID No.
 1. 2. An isolated polynucleotide which encodes a variant protein having a kinase activity substantially similar to a protein having the amino acid sequence shown in SEQ ID No. 1, wherein 1–20 amino acids are deleted, substituted, and/or added. 